All language subtitles for 12. How Devices Operate, Hubs

Now that we�ve look briefly at cabling

I�d like to explain how network devices operate.

And the first device that we're going to look at is hub

a hub is a layer 1 device in the OSI model and you would use a Cat5

unshielded twisted pair cable with an RJ-45 connector

to connect your laptop as an example to a port on a hub.

hubs aren't very popular today and have been superseded by

switches and I'll explain in a few minutes why.

But for now lets assume that you are connecting your PC to a hub.
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It�s important that you understand how a hub operate
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however because wireless operates in the same way, like a physical hub would.
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So when your connected to a wireless network you�ll often encounter
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the same issues that you would encounter when connecting to a physical hub.
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So for now lets assume that you are connecting your PC physically to a hub
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hubs have multiple ports and thus multiple devices
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can be connected to a hub at the same time.
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The number of ports available depends on the hub model
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but as you can see in both of this examples
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a hub has various ports that you can connect devices to.
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So in this topology let�s assume that you have 4 devices connected to a hub
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on ports 1 to 4, it's important to realize that a hub is a physical layer device.
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It�s not intelligent and does not understand the frames going through it.
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It's basically a multi port repeater and it will amplify
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or repeat the frames that it receives on 1 port out of all other ports.
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So it's once again simply a multi port repeater with no intelligence.
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The physical topology of a hub is a star topology.
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In a star topology you have a central device
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which in this case is a hub and devices hanging off that central device
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as spokes which resemble the spokes in the bicycle wheel.
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Each spoke devices connected to the central device with its own cable and all
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transmission or communications between devices are through the central device.
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In other words if A wants to communicate with C the traffic will flow
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through the hub and will not flow directly between the 2 devices.
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There were some major advantages to using hubs and UTP rather than 10base2.
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The first advantage is a cable break, if a cable broke in this topology
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it would only affect device A and it would not affect the rest of the network.
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In a 10base2 if a cable broke it would affect all devices in that network.
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Here however, other devices such as C and B can still communicate
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even though the cable is broken to device A.
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Another advantages that you can extend distances easily.
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A bus topology is limited in size in a 10baseT environment
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such as this, the distance between a device such as A and the hub
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needs to be 100 meters but you can extend the distance by adding another hub.
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In other words you add another multiple repeater and repeat or regenerate
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the signal to extend the distance of the network to distances greater than 100 meters.
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So in this example, E could be 100 meters away from its hub
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and the 2 hubs could be 50 meters apart.
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So in this example we've extended the network
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further than the restriction of a 100 meters.
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So device E could be 100 meters from its hub
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it could be a cable length a 50 meters between the 2 hubs
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and A could be a 100 meters away from its hub.
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A network now has a length of 250 meters
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which is well over the limitation of a 100 meters.
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Now their are restriction on the number of hubs
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that you can daisy chain together, but the point is, it's possible
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to extend the topology by adding more hubs and more devices to the network.
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These were therefore great reasons to move away from 10base2
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and 10base5 and implement UTP or untwisted pair networks using hubs.
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Another advantage is that UTP cabling is cheaper and easier to manage
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and therefore it became common to use
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hubs and 10baseT rather than 10base2 or 10base5 in the past.